全無機鈣鈦礦量子點應用於有機發光二極體之研究

鈣鈦礦量子點具可藉溶液法製備、易加工、波長可調性、量子效率高等優點，極適合光電領域之應用，如發光二極體(light-emitting diode; LED)、量子點式有機發光二極體(quantum dots light-emitting diode; QLED)、雷射、光感測器(photodetector)、太陽能電池(solar cell)等方面之應用潛能。銫鉛鹵素鈣鈦礦量子點(CsPbX3)，因其具半高寬15－40 nm之窄譜帶與高量子效率之優勢，而被視為應用於廣色域顯示器最具希望之窄譜帶綠色螢光材料。然因量子點存在表面缺陷、熱穩定性差與液態不易封裝之缺點，使其於量子點式有機發光二極體之應用受限。本研究乃藉由硫氰酸根鹽類修飾鈣鈦礦量子點表面以獲得高量子效率之窄譜帶銫鉛鹵素鈣鈦礦量子點螢光材料。修飾後之銫鉛鹵素鈣鈦礦量子點與未修飾之量子點相比，其絕對量子效率將提升約1.5倍。而其鈍化機制以硫氰酸根離子吸附鈣鈦礦量子點表面過剩之鉛離子並使表面缺陷降低，且比較銫鉛鹵素鈣鈦礦量子點其修飾前後之晶格結構，顯示晶相與結構皆無變化，表示以硫氰酸根離子修飾鈣鈦礦表面不僅能提升量子效率且不影響其結構。此外，藉硫氰酸根鹽類作為表面修飾之藥品，皆可運用於紅光、綠光與藍光之銫鉛鹵素鈣鈦礦量子點上。此外，以摻錫之鈣鈦礦量子點CsPb0.67Sn0.33Br3作為母液並與硫氰酸銨修飾後之樣品比較，因鈣鈦礦量子點表面具許多有機配體將影響製成元件時之成膜性，如十八烯、油酸與油胺，此三種溶劑皆影響元件放光層之成膜性與導電性，故先須藉丙酮去除表面過量之有機配體，藉以優化其放光層，於元件上將具更佳之表現。本研究經由硫氰酸鹽類進行表面修飾後之樣品其光譜相較於母液無明顯紅移之現象，並顯示量子點之間無明顯聚集之現象，其鈣鈦礦量子點仍為立方體之結構，綜合以上數據之結果顯示修飾後之樣品不僅能提升效率並減少量子點團聚，修飾後之樣品將可於未來應用於有機式發光二極體。

關鍵字

鈣鈦礦；銫鉛鹵素；量子點；發光二極體；表面修飾

並列摘要

White light-emitting diodes (LEDs) is widely used as backlighting components in the modern liquid-crystal display (LCD). For high-quality backlight, color saturation and color gamut are the key indicators, which affect the color performance display devices. Perovskite CsPbBr3 quantum dots (QDs) are regarded as the most promising narrow-band green-emitting material for wide-color-gamut backlight displays because of their high photoluminescence quantum yield (PLQY) and the narrow-band emission with a full width at half maximum (FWHM) of ∼20 nm. Despite their growing popularity, CsPbBr3 QDs have several shortcomings such as the existence of surface trap states, poor thermal and aqueous stability, and the solution QDs are unsuitable for direct use in on-chip white LEDs. Here, the surface treatment of perovskite CsPbBr3 QDs with thiocyanate salts (SCN-) toward high brightness and stable narrow-band green emission was investigated. After the treatment, a high quantum yield and stable narrow-band perovskite CsPbX3-SCN was obtained. The product exhibited several advantages, including high absolute PLQY of 94%, enhaced photoluminescence intensity, and air stability. Moreover, CsPbBr3-SCN perovskite QDs are potential emitters for QLED electroluminescent displays. However, balancing their performance and their environmentally friendly property is challenging. To achieve such balance, we demonstrated an easy hot-injection method to synthesize Cs(Pb1-xSnx)Br3 QDs by partially replacing the toxic Pb2+ with the highly stable Sn4+. Meanwhile, the absolute PLQY of Cs(Pb0.67Sn0.33)Br3 QDs increased from 45% to 83% compared with CsPbBr3. Based on a femtosecond transient absorption, time-resolved PL, and single-dot spectroscopies, we conclude that the PLQY enhancement is due to the reduction of trion formation in perovskite QDs with Sn4+ substitution. Moreover, the CsPbBr3-SCN solution that surface treatment with thiocyanate salt increased the performance of QLED devices based on these highly luminescent cesium lead halide perovsike QDs, exhibiting a central emission wavelength of 516 nm, a current efficiency of 4.2 cd/A, and an external quantum efficiency of 1.4% which is the higher values among the CsPbBr3 perovskite QLED devices.

並列關鍵字

perovskites ； cesium lead halide ； quantum dots ； light-emitting diode ； surface treatment.

參考文獻

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